There where 6 different major units shown there and a couple of minor ones. That first one isn't actually doing any rail changing, it's just picking up old ties and replacing them with the new ones. The second one is the guys putting the Pucks and Clips into place, the little machine after is squeezing the clips into place. The undercutter pulls the old ballast, screens it, adds what's needed to fill the cribs then continues along. after that is a HUGE ballast regulator moving the ballast back up where it's needed/usable. Then comes a C.A.T, or Continuous Action Tamper, it takes care of surface and alignment then squeezes the ballast back under the ties. Then to add what's needed again a ballast train. What they don't show is a stabilizer and another regulator to do the final settling and finish work.